The invention relates to novel crystalline silicates and to a process for their preparation. The invention further relates to the use of these silicates, inter alia, as adsorbing and extracting agents, as drying agents, as ion exchangers and as catalysts or catalyst carriers for various catalytic processes, in particular for the catalytic preparation of aromatic hydrocarbons.
The crystal structure of the silicates according to the invention has interstices of molecular dimensions, which are usually filled with hydration water. After at least partial dehydration the silicates can be used as efficient adsorbing agents, the adsorbed molecules being retained in the interstices. These interstices are accessible via openings in the crystal structure. Depending on the cross-sectional area of these openings the dimensions and the shape of the molecules, which can be adsorbed, and restricted. This enables certain molecules to be separated from mixtures on the basis of molecular dimensions, certain molecules being adsorbed by the silicates whereas others are rejected. Materials having this property are usually referred to as molecular sieves. This property of the silicates according to the invention may be utilized when they are used as catalysts or catalyst carriers in selectively carrying out processes in which either from a mixture of compounds differing in structure only the compounds having a specific structure are converted, or from a compound a compound only compounds having a specific structure are formed, as a result of the fact that only compounds having that specific structure can, respectively, penetrate into or leave the silicates.
The silicates according to the invention are characterized as a class of compounds by their thermal stability, their adsorption behavior and their overall composition. The crystallinity of the various compounds follows from the fact that they all show a clear X-ray powder diffraction pattern.